1. Technical Field of the Invention
This invention pertains to inventive methods of manufacturing a semiconductor device for improving device performance, and to the resulting unique high-performance device structure. In particular, this invention has improved charge mobility in FET devices by structurally imposing tensile and compression forces in a device substrate during device fabrication.
Within the field of semiconductor device design, it is known that mechanical stresses within the device substrate can modulate device performance. Individual stress tensor components affect device behavior of PFETs and NFETs differently. Previous improvements that utilized stress enhancements tended to focus on one or the other type of device outside of a practical performance environment, such as in an IC chip. In order to maximize the performance of both PFETs and NFETs within IC chips, the stress components need to be engineered and applied differently, yet simultaneously. In the present invention we show fabrication methods and resulting structures that have imposed the appropriate stress fields needed to improve the performance of a single device and of at least two devices simultaneously in a common substrate.
2. Description of the Prior Art
Hamada et al, IEEE Transactions on Electron Devices, Vol. 38 No. 4, A New Aspect of Mechanical Stress Effects in Scaled MOS Devices (April 1991) show data correlating weight induced (bending a sample silicon chip) longitudinal and transverse tensile and compressive stress with Transconductance deviation. Within the PFET device a longitudinally applied uniaxial compressive stress had an effect reversed from the effect induced on an NFET. This data can be interpreted such that if you apply an in-plane biaxial tensile stress, the NFET device performance will improve about two-fold as compared to that of a uniaxial tensile situation, while the PFET experiences no change because the longitudinal and transverse tensile stress effects cancel each other out.
In the Symposium on VLSI Technology Digest of Technical Papers (2001), Rim et. al. shows that, using strained Si which has in-plane biaxial tensile stress, improvements occurred for an NFET with a 70% increase in electron mobility. Prior known solutions and methods using mechanical stress for device performance enhancement could not improve both NFETs and PFETs simultaneously. Moreover, prior solutions do not address the feasibility of any kind of device structures or methods of fabricating them.